. Electric railway journal . the per-centages of ties that need replacement at proportionateintervals in the lives of any two groups. The comparisons are based on forty-three groups,including 42,000 ties of many species, some untreatedand some treated. For any of these groups, the per-centage of renewals in relation to the percentage ofaverage life is fairly represented by the curve shown. This curve answers several valuable purposes. It canbe used in estimating the average life of a group ofties long before all the ties in the group have beenremoved, also to show the number of replacements th
. Electric railway journal . the per-centages of ties that need replacement at proportionateintervals in the lives of any two groups. The comparisons are based on forty-three groups,including 42,000 ties of many species, some untreatedand some treated. For any of these groups, the per-centage of renewals in relation to the percentage ofaverage life is fairly represented by the curve shown. This curve answers several valuable purposes. It canbe used in estimating the average life of a group ofties long before all the ties in the group have beenremoved, also to show the number of replacements thatwill be necessary during a given year. As an example, assume that out of a group of 1,000ties, 200, or 20 per cent, have been removed at the end offour years. From the curve it will be seen that 20 percent of a group is usually removed at about 77 per centof the average life. The average life of this group, then,will be years. Further computation shows that thenumber of replacements to be expected during the fifth 100. 30 40 00 00 70 BO 90 100 UO 120 ISO HO 150 160 170 180 190 Average Lite - PercentTIE RENEWALS IN RELATION TO AVERAGE LIFE year is about 350, the sixth year 300, the seventh 100,and that at the end of nine years practically all the tiesin the group will have been removed. Thus, with the aid of the curve, it is possible to pre-dict the average life of any group of ties even whilemost of them are still in service. American Association News ASSOCIATIONS PUBLICITY PLAN AS OUTLINED—ENGINEERING AND OTHER ASSOCIATIONREPORTS ARE BEING WHIPPED INTO FORM—EXECUTIVE COMMITTEE SELECTSATLANTIC CITY FOR CONVENTION, WHICH WILL BE HELDIN NEW HALL ADJOINING BOARDWALK Atlantic City Gets 1921 Convention ONCE more Atlantic City has been chosen as thelocation of the annual convention of the associ-ation. The 1921 convention will be held during theweek beginning Oct. 3. In view of the fact that thereare to be no exhibits in connection with this yearsconvention arrangements hav
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